The DASP of the present invention are used in both regular and synthetic lubricants, where they lower surface tension from 30 dynes/cm2 to below 25 dynes/cm2 at concentrations of less than 5% by weight.
Defining the term “synthetic lubricant” in general it refers to a lubricant or grease whose basestock has been manufactured by chemical synthesis or organic reaction, as opposed to being extracted or refined from naturally occurring oils. In many respects synthetics represent a different approach altogether from conventional petroleum based oils in that their molecular structures are custom designed and tailored to meet specific performance targets.
Most lubricants consist of a basestock and various additives selected to improve or supplement the basestock's performance. The basestock is the primary component, usually 70 to 99% of the finished oil and its properties play a vital role. To a great degree the structure and stability of the basestock dictate the flow characteristics of the oil and the temperature range in which it can operate, as well as many other vital properties such as volatility, lubricity, and cleanliness. Additives enhance these properties or impart new ones, such as improving stability at both high and low temperatures, modifying the flow properties, and reducing wear, friction, rust and corrosion. The basestock's and additives work together and must be carefully selected and balanced to allow the finished oil to do its intended job, which includes protecting moving parts from wear, removing heat and dirt, preventing rust and corrosion, and improving energy efficiency. Since the basestock is the dominate component with the most important role, one obvious way to make a better oil is to start with a better basestock. That is exactly what synthetic oils endeavor to accomplish.
Conventional petroleum basestocks or mineral oils begin with crude oil, a mixture of literally hundreds of different molecules derived from the decomposition of prehistoric plant and animal life. The lighter more volatile components of crude oil are stripped away to make gasoline and other fuels, and the heaviest components are used in asphalt and tar. It's the middle cuts that have the right thickness or viscosity for lubricants, but first they must be cleaned up; undesirable components such as waxes, unsaturated hydrocarbons, and nitrogen and sulfur compounds must be removed. Modern processing techniques do a pretty good job of removing these undesirable components, well enough for well over 95% of the world's lubricant applications, but they cannot remove all of the bad actors. And it's these residual “weak links” that limit the capabilities of mineral oils, usually by triggering breakdown reactions at high temperatures or freezing up when cold. These inherent weaknesses limit the temperature range in which mineral oils can be used and shorten the useful life of the finished lubricant.
Synthetic basestocks, on the other hand, start from relatively pure and simple chemical building blocks, which are then reacted together or synthesized into new, larger molecules. In fact the entire formulation approach is different: instead of trying to clean up a naturally occurring chemical soup to acceptable levels with a constant eye on cost, the synthetic molecular engineer is able to focus on optimum performance in a specific application with the knowledge that he can build the necessary molecules to achieve it. Since synthetics cost considerably more than petroleum based basestocks, they are generally reserved for problem applications where conventional oils fail, or where the efficiency benefits of synthetics recoup the initial cost.
The use of synthetic basestocks to solve lubrication problems is not new. Various synthetics were developed and used extensively during the second world war to prevent the oil from freezing in the army tanks during winter combat. After the war, synthetics were found to be essential for the new jet engines which ran too hot for mineral oils, causing them to burn off rapidly and leave deposits. These jet engines also had to be able to restart at high altitudes where temperatures were often −50° F., so the oil had to pumpable at very low temperatures as well as surviving the searing temperatures within the engine. Indeed the modern jet engine would not exist today if not for the simultaneous development of synthetic basestock technology in the 1950s, and today virtually every jet engine in the world operates exclusively on synthetic lubricants.
During the 1960s and 70s, synthetics moved steadily into severe industrial applications where they solved high temperature deposit problems with air compressors and oven conveyor chains, and low temperature flow problems in arctic climates.
Synthetic automobile motor oils were introduced in the early 1970s with such fantastic performance claims that they initially turned the auto manufacturers and oil companies against the new unproven products. While most claims were directionally valid, the levels of improvements are exaggerated to the point of fostering a “snake oil” reputation. Over the ensuing years, the true benefits of synthetic motor oils were identified and quantified to industry satisfaction and include better high temperature stability, excellent low temperature flow characteristics, lower volatility, increased fuel efficiency, and extended life capability. Today car manufacturers and oil companies alike readily acknowledge the superior performance of synthetic motor and gear oils, especially in fleet or severe duty usage.
Today the use of synthetic lubricants is accepted, widespread, and rapidly growing as their capability and cost efficiency benefits become better known worldwide. Jet aircraft use synthetic oils in the engines, hydraulic systems, instruments and landing gears; compressors use synthetics in the crankcase and cylinders; refrigeration systems use synthetics with the new environmentally friendly refrigerants; truck fleets use synthetics in the engine, transmission, and gear box; and the list goes on and on. Wherever a problem exists with mineral oils or a potential for improved cost efficiency uncovered, there is a synthetic lubricant ready and able to step in and lower the cost of total lubrication.
Some properties are inherent in the class, such as high temperature thermal and oxidative stability, low volatility, high flash and fire points, and low temperature fluidity. Others can be varied according to need such as biodegradability, lubricity, hydrolytic stability, viscosity index, and coking tendencies. Esters are more and more commonly used in synthetic lubricants, but can degrade as a function of temperature. This degradation results in several oxidation products which accelerate the rate of degradation. The beginning of degradation is in fact a catalyst in the rapid degradation.
Additionally, the ability to lower surface tension of the lubricant below 30 dynes/cm2 has been elusive since organic materials from which they are based have this value as the lower limit of surface tension achievable. Lower surface tension makes for better lubrication, and slip of metal parts, resulting in improved lubrication. Improved lubrication results in lower operating temperatures and improved miles per gallon.
Lower surface tension can only be achieved by using dimethyl silicones (also known as silicone fluids), but these polymers are not soluble in oil bases and have not been used. The present invention relates to including two very key groups on the silicone polymer, the first an alkyl group, improving the solubility of the silicone in oil, and also a very limited crosslink density that despite clarity in the oil results in the lowest free energy of the oil to be when the silicone polymer is pushed to the oil metal interface, where it surprisingly lowers surface tension.
PAOs (poly alpha olefins) have been used as additives to lubrication oils, but due to PAOs lower cost and their formulating similarities to mineral oil. However these materials do not lower surface tension below the critical 30 dynes/cm2.
The new frontier for lubricants is the industrial marketplace where the number of products, applications, and operating conditions is enormous. In many cases, the very same equipment, which operates satisfactorily on typical oil in one plant could benefit greatly from the use of a DASP modified lubricant in another plant where the equipment is operated under more severe conditions. This is a marketplace where old problems or new challenges can arise at any time or any location. The high performance properties and custom design versatility of DASP lubricants is ideally suited to solve these problems. Lubricants based upon DASP have niches in the industrial market such as reciprocating air compressors and high temperature industrial oven chain lubricants.
The ability of the DASP molecules to get to the surface, and lower surface tension causes the molecules tend to line up on the metal surface creating a film which requires additional energy (load) to penetrate. The result is a stronger film which translates into higher lubricity and lower energy consumption in lubricant applications.
The structure of the DASP makes them good solvents and dispersants. This allows them to solubilize or disperse oil degradation by-products, which might otherwise be deposited as varnish or sludge, and translates into cleaner operation and improved additive solubility in the final lubricant.
Another important difference between esters and PAOs is the incredible versatility in the design of DASP molecules due to the ability to tailor molecules. The performance properties that can be varied to include viscosity, viscosity index, volatility, high temperature coking tendencies, biodegradability, lubricity, hydrolytic stability, additive solubility, and seal compatibility.
DASP molecules unlike other esters used in synlube applications, do not tend to swell and soften most elastomer seals, solving a major problem.
U.S. Pat. Nos. 2,396,191; 2,936,320; 3,021,357; 3,637,501; 3,912,640; and 4,080,303 are illustrative of prior art attempts to formulate lubricants containing esters of aromatic polycarboxylic acids.
U.S. Pat. No. 3,637,501 describes neo-carbon containing polycarboxylic acid esters wherein the ester groups on the aromatic nucleus contain at least one carbon atom connected directly to four other carbon atoms.
U.S. Pat. No. 5,288,432 to Jung issued Feb. 22, 1994, incorporated herein by reference teaches high temperature synthetic lubricants and related engine lubricating systems. These high temperature lubricant composition comprise a polycarboxylic acid esters and organophosphorus compounds is described. This composition is useful for lubricating very high temperature diesel engines. A method of rectifying used lubricant compositions is also described.
The number of lubricant patents and the continued research on such materials is a testimony to the severity of the problem and the long felt need for improvement. The lack of silicone polymers used to address the shortcomings of oil based materials shows that one of ordinary skill in the lubricating art would not look to silicones to solve these problems. This is do the inherent insolubility of all silicones that are not made following the teachings of this invention to be soluble in base stock and the inability to achieve the desired surface tension reduction.
DASP are most useful for high temperature lubricant applications. Moreover, we considered them superior in thermal properties, providing the best balance of high temperature stability and lubrication performance.